In variable-capacity superchargers, a variable nozzle unit is provided between a turbine scroll channel and a turbine wheel (a turbine impeller) in a turbine housing. The variable nozzle unit is provided at an outer circumferential side of the turbine wheel in the turbine housing. The variable nozzle unit is generally provided with first and second nozzle rings that are provided to be apart from each other in an axial direction of the turbine wheel, and a plurality of variable nozzles that are sandwiched between the first nozzle ring and the second nozzle ring and are disposed at equal intervals in a circumferential direction. The first nozzle ring is provided at a bearing housing side in the axial direction of the turbine wheel relative to the turbine wheel. The second nozzle ring is disposed to surround an outer circumference of the turbine wheel. The pluralities of variable nozzles have nozzle shafts extending in the axial direction of the turbine wheel, and the nozzle shafts are rotatably supported by the first and second nozzle rings. In the variable nozzle unit having the above constitution, the plurality of variable nozzles are synchronized and rotated in an opening direction, and thereby a channel area of an exhaust gas supplied to the turbine wheel side can be increased. The plurality of variable nozzles are synchronized and rotated in a narrowing direction, and thereby the channel area of the exhaust gas can be increased. In this way, in the variable-capacity supercharger, the channel area is changed to control a supercharging pressure by the variable nozzles. Thereby, supercharging efficiency can be properly maintained.
In this variable-capacity supercharger, for the purpose of improving the supercharging efficiency, various constitutions for preventing leakage of the exhaust gas have been reviewed. For example, in Patent Literature 1, a seal cover is provided at a rear surface side of the second nozzle ring which is opposite to a surface facing the first nozzle ring. Thus, a constitution for preventing leakage of the exhaust gas from the turbine scroll channel to an outlet side of the turbine wheel is suggested.